Intracorporal medical devices have been developed and used to navigate and access the tortuous vascular anatomy and other hollow conduits of a mammalian body. Some of these devices include intravenous guidewires, stylets, intravenous catheters and related devices like endoscopes and colonoscopes that have a predetermined degree of flexibility and may have straight or pre-formed, shaped ends to guide the device through the anatomical conduit. Of the devices that are employed to reach vascular blockages, each has certain advantages and disadvantages. Many fall short of desired performance before reaching a vascular blockage because of a prolapse at a vascular bifurcation, an inability to enter a bifurcation or to be directed to the site of therapy. Others may reach an occlusion but then require a different device to be introduced before crossing the stenosis. The medical industry has striven to reach a balance between the flexibility required to negotiate around tortuous pathways and the rigidity necessary to stabilize a catheter's advancement. Many intravenous interventional guidewires provide directability, flexibility or stiffness but fail to do all or a combination at the same time. These products typically have pre-formed flexible distal ends that provide minimal directability but not true directability, flexibility and stiffness combined, which would be the most useful advantage. Additionally, most physicians must use a series of different diameter guidewires to perform one procedure, creating a procedure that costs additional time, money and risks patient safety from vascular injury.
Accessing occlusions having relatively sharp angles and passage constrictions using conventional guidewires having pre-formed “J” shapes or angled distal ends requires rotating the guidewire while simultaneously moving it proximally and distally. This action can cause damage to the fragile endothelial cell layer lining blood vessels. Additionally, conventional guidewires can lose their ability to be rotated when the flexible distal ends enter vessels of reduced diameter. Rotation of the guidewire following inserting the distal end into a vessel having a reduced diameter may produce relatively high frictional forces between the walls of the small vessels and the guidewire. A desirable device would therefore require reduced rotation and increased ability to advance in a forward or distal direction through tortuous anatomies.
Another undesirable characteristic of conventional guidewires is the inability to support a catheter at the flexible, tapered, distal end. When a catheter is advanced over a guidewire toward a vascular location in and close to a bifurcation, the catheter tends to proceed in a straight line rather than following the guidewire. Further, the natural pulsation of the vascular system of a living animal can cause a conventional guidewire to move within the body and thereby lose its distal location. To address the undesirable characteristic of a conventional guidewire that allows a catheter to prolapse, a guidewire that is stiffer on the distal end yet still able to be directed into a vascular bifurcation would prevent the catheter from proceeding in a straight line. It would also allow a stiffer catheter or a catheter with a larger diameter to be used.
Physicians generally have four objectives when using such vascular devices: (1) To reach the occlusion; (2) To reach the occlusion without causing vascular damage; (3) To cross the occlusion once it is reached; and (4) To reach the occlusion and cross it in as little time as possible. A device able to accomplish all four objectives would be extremely advantageous. It is not uncommon for a physician to place a catheter somewhere in a vessel and exchange the first guidewire with one or more secondary guidewires having progressively stiffer distal ends to prevent prolapse of the devices placed over the guidewire(s). These four objectives would be resolved by a guidewire stiff enough to be advanced through the vasculature and yet be directed into branched vessels with minimal rotational torque and minimal sliding back and forth in proximal and distal directions to enter a bifurcation. Yet another advantage would be having a guidewire stiff enough to be pushed and yet be directed into branched vessels with minimal torquing.
Vascular occlusions defined as Chronic Total Occlusions are blockages that can occur anywhere in a patient's vascular system, including coronary, carotid, renal, iliac, femoral, cerebral, popliteal and other peripheral arteries.
U.S. Pat. No. 4,676,249 to Arenas et al. discloses a guidewire having a moving internal member to provide stiffness when required, but does not disclose a directable distal end or the ability to cross occlusions. Another, U.S. Pat. No. 5,542,434 to Imran et al., discloses a longitudinally movable core wire made of a memory metal alloy that stiffens when subjected to thermal energy. Yet another, U.S. Pat. No. 5,605,162 to Mirzaee et al., uses a pull wire to draw the distal coil proximally to stiffen the distal end. These devices allow the wire to become stiff and yet torquable when desired, but fail when a catheter needs to be slid over the device. Both devices are deficient when they reach an occlusion with heavily calcified plaque in that they do not have sufficient stiffness to cross the occlusion.
For all these and other reasons there is a clear need for a guidewire that can vary the shape of its distal end, is relatively stiff and also has the ability to cross an occlusion.